24 research outputs found
Spin photonics on chip based on a twinning crystal metamaterial
Two-dimensional photonic circuits with high capacity are essential for a wide
range of applications in next-generation photonic information technology and
optoelectronics. Here we demonstrate a multi-channel spin-dependent photonic
device based on a twinning crystal metamaterial. The structural symmetry and
material symmetry of the twinning crystal metamaterial enable a total of 4
channels carrying different transverse spins because of the spin-momentum
locking. The orientation of the anisotropy controls the propagation direction
of each signal, and the rotation of the E-field with respect to energy flow
determines the spin characteristics during input/output coupling. Leveraging
this mechanism, the spin of an incident beam can be maintained during
propagation on-chip and then delivered back into the free space, offering a new
scheme for metamaterial-based spin-controlled nano-photonic applications
Effect of growth temperature on the morphology and phonon properties of InAs nanowires on Si substrates
Catalyst-free, vertical array of InAs nanowires (NWs) are grown on Si (111) substrate using MOCVD technique. The as-grown InAs NWs show a zinc-blende crystal structure along a < 111 > direction. It is found that both the density and length of InAs NWs decrease with increasing growth temperatures, while the diameter increases with increasing growth temperature, suggesting that the catalyst-free growth of InAs NWs is governed by the nucleation kinetics. The longitudinal optical and transverse optical (TO) mode of InAs NWs present a phonon frequency slightly lower than those of InAs bulk materials, which are speculated to be caused by the defects in the NWs. A surface optical mode is also observed for the InAs NWs, which shifts to lower wave-numbers when the diameter of NWs is decreased, in agreement with the theory prediction. The carrier concentration is extracted to be 2.25 Ă— 1017 cm-3 from the Raman line shape analysis. A splitting of TO modes is also observed
Optical vortices enabled by structural vortices
The structural symmetry of solids plays an important role in defining their
linear and nonlinear optical properties. The quest for versatile,
cost-effective, large-scale, and defect-free approaches and materials platforms
for tailoring structural and optical properties on demand has been underway for
decades. We experimentally demonstrate a bottom-up self-assembly-based organic
engineered material comprised of synthesized molecules with large dipole
moments that are crystallized into a spherulite structure. The molecules align
in an azimuthal direction, resulting in a vortex polarity with spontaneously
broken symmetry leading to strong optical anisotropy and nonlinear optical
responses. These unique polarization properties of the judiciously designed
organic spherulite combined with the symmetry of structured optical beams
enable a plethora of new linear and nonlinear light-matter interactions,
including the generation of optical vortex beams with complex spin states and
on-demand topological charges at the fundamental, doubled, and tripled
frequencies. The results of this work are likely to enable numerous
applications in areas such as high-dimensional quantum information processing,
with large capacity and high security. The demonstrated spherulite crystals
facilitate stand-alone micro-scale devices that rely on the unique micro-scale
spontaneous vortex polarity that is likely to enable future applications for
high-dimensional quantum information processing, spatiotemporal optical
vortices, and a novel platform for optical manipulation and trapping
ASXL1 interacts with the cohesin complex to maintain chromatid separation and gene expression for normal hematopoiesis
ASXL1 is frequently mutated in a spectrum of myeloid malignancies with poor prognosis. Loss of Asxl1 leads to myelodysplastic syndrome-like disease in mice; however, the underlying molecular mechanisms remain unclear. We report that ASXL1 interacts with the cohesin complex, which has been shown to guide sister chromatid segregation and regulate gene expression. Loss of Asxl1 impairs the cohesin function, as reflected by an impaired telophase chromatid disjunction in hematopoietic cells. Chromatin immunoprecipitation followed by DNA sequencing data revealed that ASXL1, RAD21, and SMC1A share 93% of genomic binding sites at promoter regions in Lin-cKit+ (LK) cells. We have shown that loss of Asxl1 reduces the genome binding of RAD21 and SMC1A and alters the expression of ASXL1/cohesin target genes in LK cells. Our study underscores the ASXL1-cohesin interaction as a novel means to maintain normal sister chromatid separation and regulate gene expression in hematopoietic cells
An abnormal bone marrow microenvironment contributes to hematopoietic dysfunction in Fanconi anemia
Fanconi anemia is a complex heterogeneous genetic disorder with a high incidence of bone marrow failure, clonal evolution to acute myeloid leukemia and mesenchymal-derived congenital anomalies. Increasing evidence in Fanconi anemia and other genetic disorders points towards an interdependence of skeletal and hematopoietic development, yet the impact of the marrow microenvironment in the pathogenesis of the bone marrow failure in Fanconi anemia remains unclear. Here we demonstrated that mice with double knockout of both Fancc and Fancg genes had decreased bone formation at least partially due to impaired osteoblast differentiation from mesenchymal stem/progenitor cells. Mesenchymal stem/progenitor cells from the double knockout mice showed impaired hematopoietic supportive activity. Mesenchymal stem/progenitor cells of patients with Fanconi anemia exhibited similar cellular deficits, including increased senescence, reduced proliferation, impaired osteoblast differentiation and defective hematopoietic stem/progenitor cell supportive activity. Collectively, these studies provide unique insights into the physiological significance of mesenchymal stem/progenitor cells in supporting the marrow microenvironment, which is potentially of broad relevance in hematopoietic stem cell transplantation
Artificial Generation of High Harmonics via Nonrelativistic Thomson Scattering in Metamaterial
High harmonic generation allows one to extend the frequency of laser to a much broader regime and to study the electron dynamics of matters. However, severely limited by the vague high-order process in natural material and the unfriendly state of the commonly applied gas and plasma media, the ambitious goal of custom-design high harmonics remains exceptionally challenging. Here, we demonstrate that high harmonics can be artificially designed and tailored based on a metamaterial route. With the localized reconstruction of magnetic field in a metamaterial, the nonlinear Thomson scattering, a ubiquitous electromagnetic process which people used to believe that it only occurs with the relativistic velocity, can be stimulated in a nonrelativistic limit, which drives anharmonic oscillation of free electrons and generates high harmonics. An explicit physical model and the numerical simulations perfectly demonstrate the artificial generation and tailoring of the high harmonics. This novel mechanism is entirely dominated by the artificial structure instead of the natural nonlinear compositions. It not only provides unprecedented design freedom to the high harmonic generation but breaks the rigorous prerequisite of the relativistic velocity of the nonlinear Thomson scattering process, which offers fascinating possibilities to the development of new light source and ultrafast optics, and opens up exciting opportunities for the advanced understanding of electrodynamics in condensed matters
Research on fatigue damage correction coefficient of main truss members of railway suspension bridges
Steel truss girder suspension bridges are gradually applied to long-span railway bridges. The fatigue damage correction factor is an important parameter for fatigue calculation, however the research on the coefficient is limited to small-span bridges. This paper analyzes force characteristics of main truss members, calculates the fatigue damage correction coefficient of truss members, and studies the influences of train loading length, annual traffic level of fatigue damage correction coefficient. The main conclusions are as follows: (1) The influence line and fatigue stress characteristics of the main truss members were studied; the stress range of members under tension or mainly under tension is analyzed, and the stress ranges and ratios between dead and live loads in main truss members are investigated. The results show that the maximum stress range of the bottom chord is 182Â MPa, the ratios of dead to live loads of about 90 % of bottom chords and diagonal web members exceed the current specifications, and stress ratios of about 10 % of bottom chords and diagonal web members exceed the current specifications. (2) The fatigue damage correction coefficients of main truss members under different train loading lengths and annual traffic levels are calculated and recommended. The research results provide a basis for updating and supplementing the railway steel bridge code
Absorption modulation of terahertz metamaterial by varying the conductivity of ground plane
Most research focuses on varying the resonator and dielectric spacer to configure the absorption and resonant frequency of terahertz (THz) metamaterial absorbers (MAs), where a metal ground plane is used as a perfect reflector of incident THz waves. In this paper, we modulate the MAs absorption by varying the conductivity of the ground plane. Two THz MAs were fabricated by replacing the gold ground planes with cobalt silicide films, and the measured absorptivity decreases by 4% for the electric resonance and increases by 44% for the dipole resonance. Our quantitative analysis reveals that when the conductivity of the ground plane decreases from 1.8 x 10(7) S/m to 3.0 x 10(5) S/m, the absorptivity of the electric resonance decreases by 23%, while that of the dipole resonance increases by 62%. Our approach also provides a practical method to measure the electric conductivity of conductive films in the THz regime. (C) 2014 AIP Publishing LLC